1. Field of the Invention
This invention relates to a process for improving the properties of cellulose fiber, particularly the dyeing properties of cellulose fiber, and to a process for dyeing the same.
2. Description of the Prior Art
In general, disperse dyes have excellent color affinity to synthetic fibers, especially to polyester fibers, but have poor affinity to cellulose fibers. Thus, it is not possible to dye a product such as mixed yarn or union cloth composed of cellulose and synthetic fibers with disperse dyes. Such products can be dyed by a process in which the disperse dye is used in combination with a direct dye, reactive dye, soluble vat dye, or vat dye; the synthetic fiber portions being first dyed by the disperse dye and then the cellulose fiber portions being dyed by the direct dye, reactive dye, soluble vat dye or vat dye. The process, however, has disadvantages because it is intricate, time-consuming and gives a product with poor color fastness.
The above-mentioned product can also be dyed by a pigment dyeing process and by a process wherein Dyblen (registered trademark) dyes are used. The pigment dyeing process has the advantages that simultaneous printing can be carried out and operations are simple, but has the disadvantages that it gives a product having poor color fastness to rubbing and having a rough, coarse tactility. The Dyblen dyeing process has the advantage that simultaneous printing can also be carried out, but has the disadvantage that it gives a product having poor color fastness. Thus, none of the conventional processes provide good dye fastness to a product in the form of mixed yarns or union cloth of both cellulose fibers and polyester synthetic fibers. Those skilled in the art, therefore, have sought a process which can give color fastness to a product composed of both cellulose fibers and polyester synthetic fibers. In accordance with this general trend, it was attempted to determine whether or not there is a process wherein the cellulose fibers can be dyed with disperse dyes to give a product having good color fastness while retaining good tactility in the cellulose fibers.
It is known that cellulose fibers can be modified to give a product which has good affinity to disperse dyes and which can be dyed by disperse dyes when the cellulose fibers are either esterified or etherified. The thus esterified or etherified product, however, usually loses its soft tactility and becomes stiff, and hence is of no practical use because it has lost an essential property of the fibers. For example, when the cellulose fibers are acylated by a fatty acid such as acetic acid, propionic acid or butyric acid, the resulting fibers can be dyed easily with disperse dyes; the resulting fibers, however, are not good in color fastness, and especially are considerably degraded in color fastness to washing, although the resulting fibers are more or less improved in color affinity. In order to improve the color fastness of the resulting fibers, it is required either to acylate the cellulose fibers to a higher degree or to use a fixing agent at the time of dyeing. However, if the cellulose fibers are highly acylated or if a fixing agent is used, then the resulting fibers lose their characteristic tactility. Thus, conventionally acylated cellulose fibers did not come to have practical use.
In copending United States application, Ser. No. 661,825, filed Feb. 26, 1976, it is disclosed that benzoylation of cellulose fibers may be carried out, wherein the cellulose fibers are firstly treated with an alkaline solution and then with a benzoyl chloride, or wherein the cellulose fibers are reacted with benzoyl chloride in the presence of a basic medium such as pyridine, quinoline or dimethyl aniline. The resulting fibers, however, tend to lose the soft and flexural tactility characteristic of the cellulose fibers and hence become stiff and coarse.
To obtain cellulose fibers which can be easily dyed by disperse dyes and which have good tactility, it was attempted to esterify the cellulose fibers with various acids such as acetic acid and benzoic acid, and also to etherify, for example, cyanoethylate the cellulose fibers. As a result, it was found that cellulose fibers can be converted into a product, without deteriorating both the tactility and hygroscopic property of the fibers, which can be dyed with disperse dyes in vivid color and with good color fastness, if the cellulose fibers are acylated by an aromatic acid merely on the surface thereof to have an appropriate value of substitution degree of the acyl group.
Moreover, it was confirmed that the process in which such acylation is carried out is significant in that the cellulose fibers maintain excellent tactility after they have been acylated.